In a process for producing a semiconductor device, a film is formed on a substrate to be processed such as a wafer using chemical vapor deposition (CVD) method.
The film is formed in the following manner. That is, a predetermined number of wafers are mounted on a boat. The wafers mounted on the boat are loaded into a reaction furnace. The reaction furnace is evacuated, reaction gas is introduced into the reaction furnace, and films are formed on the wafers.
After the film formation is completed, the pressure in the reaction furnace is returned to the atmospheric pressure, and the boat is unloaded. The boat is cooled in a state in which the boat is completed pulled out from the furnace. At the same time, the temperature in the reaction furnace is lowered, and gas purging (decompression N2 purging) is carried out. With the gas purging, stress of deposited film adhered to an inner wall of the reaction furnace is increased to allow a cracking to produce in the deposited film, and fine particles generated when the cracking is produced is eliminated by the gas purging (see Japanese Patent Application Laid-open Publication No. 2000-306904).